Battery sensors in the past have been made to measure the temperature, state of charge or level of electrolyte in a battery cell through various independent means.
The state of charge of a battery has previously been determined through direct voltaic measurement as shown in U.S. Pat. No. 1,338,170. State of charge measurements have also been made indirectly by measuring the conductivity and specific gravity of the electrolyte. U.S. Pat. No. 2,836,808 and 3,060,375 disclose the use of conductivity probes in battery testers. U.S. Pat. No. 3,308,366 discloses using either a conductivity probe or a float for specific gravity measurement to determine the state of charge in a battery.
Electrolyte level determination has been made using conductivity probes as shown in U.S. Pat. Nos. 3,308,366 and 2,836,808 such that when the electrolyte level drops below the sensing electrodes, the current path between the electrodes is removed which is registered through a meter response.
Temperature measurements have been effected by such means as contact indicators as disclosed, for example, in U.S. Pat. No. 1,779,946. Temperature compensating conductivity devices are shown in U.S. Pat. Nos. 2,834,937 and 3,657,731 wherein changes in the conductivity of the electrolyte over varying temperatures are automatically compensated for by comparison with a temperature controlled resistance or an incorporated heat-sensing element.
The prior art, however, fails to provide for an efficient combination of sensing elements within a unitary device, such as a battery cap and which senses the temperature, state of charge and electrolyte level in a battery cell.